Is saying "Allah suffices us, and He is the best Disposer of affairs" when feeling wronged by one's father considered an act of disobedience (uqūq), and how can one atone for that? And what is the best way to deal with one's father to avoid uqūq given the frequency of problems and clashes?

The right of a parent is great, and it is not permissible for a child to reciprocate their parent's ill-treatment with ill-treatment or disobedience. It is forbidden to supplicate against them, even if they are oppressive. As for the saying "Hasbi Allah wa ni'ma al-wakeel" (Allah is sufficient for me, and He is the best Disposer of affairs), it is not a supplication against him, but avoid saying it in his presence, as it may be understood as a supplication against an oppressor. One must avoid confrontation with the parent. If avoiding speaking and sitting with him angers him, then that is not permissible; rather, one must sit with him gently and courteously, and avoid discussions that lead to problems. If leaving him does not sadden him, then there is no harm, provided that there is no complete abandonment and one continues to inquire about him and fulfill his requests. The parent is the middle gate of Paradise, and his pleasure is from the pleasure of Allah. Therefore, it is advised to be patient with his oppression and to counter his ill-treatment with kindness, and to supplicate for his righteousness.